This invention is generally directed to imaging members and processes for the preparation thereof. More specifically, the present invention relates to layered photoconductive imaging members with excellent mechanical characteristics, and wherein belts and drums are formed comprised of a conductive substrate, a photogenerator layer and charge transport layer generated simultaneously or in rapid succession by the polymerization of macrocyclic carbonate oligomers to form polycarbonates which can function as binder resins for the photogenerating and charge transport layers. The present invention also relates to processes for the preparation of imaging members without solvents in embodiments, wherein the polycarbonate resin binder is formed simultaneously with the charge transport and photogenerating layer. Imaging members of the present invention can be sensitive to wavelengths of from about 400 to about 800 nanometers, that is from the visible region to the near infrared wavelength region of the light spectrum. Moreover, in embodiments thereof the imaging members of the present invention possess low dark decay characteristics as illustrated herein and enable developed images, both line and solid areas, of high resolution, that is with substantially no background deposits. The imaging members of the present invention can be selected for electrophotographic, especially xerographic imaging systems. These imaging members are usually prepared by first providing on a supporting substrate a photogenerating layer of, for example, trigonal selenium, and thereafter solution coating thereover from a solvent mixture a charge transport layer and polycarbonate resin, such as MAKROLON.RTM.. Thus, the polycarbonate resin binder is in the form of a polymer when selected for the preparation of the imaging member. With the invention of the present invention, in contrast and in embodiments there is selected a monomer and this monomer is converted into a polymer binder simultaneously with the coating of the charge transport layer. The advantages of the aforementioned include, for example, the use of solvents like toluene or tetrahydrofuran, rather than the toxic and environmentally damaging chlorinated, such as methylene chloride, organic solvents to form the coating. Since solution viscosity is proportional to molecular weight, and it is the coating solution viscosity that determines the concentration for any given coating technique, the use of higher solid loadings in the coating solution is readily achievable as the cyclic oligomer precursor to the polymer possesses a much lower by, for example, orders, such as 10, of magnitude solution viscosity than the polymer itself and higher solid loadings are desirable to reduce volatile organic concentrations emitted during the coating process. The processes of the present invention and imaging members thereof allow the binder to be optionally crosslinked to provide tougher and more solvent resistant coatings. Also provided are higher, 100,000 to 300,000, molecular weight polycarbonates versus about 40,000 for spray coating molecular weight polycarbonate films formed using spray or dip coating techniques. The use of a solvent for forming a photoreceptor film may be avoided entirely with the present invention in embodiments by coating the cyclic oligomers and transport molecule mixture as a melt or a powder before curing the cyclic oligomers to the high molecular weight polymer. Additionally, by using mixtures of different structured cyclic oligomers high molecular copolymers of exact stoichiometry can be obtained that are not readily effectively obtained by either the known interfacial or melt transesterification processes for producing polycarbonates. Photogenerating pigments are usually milled in an organic solvent to obtain small, about 0.1 to 0.2 micron, particle size and preferred morphology. The polymer binder is selected with consideration of the aforementioned milling, phthalocyanine pigments, for example, are often converted to less sensitive morphologies by chlorinated solvents and thus the use of polymers that are only soluble in these solvents, such as polycarbonate, is precluded. However, polycarbonates because of their clarity and toughness are otherwise an acceptable polymer binder. This invention allows the use of polycarbonate as a binder for photogenerating pigments, since for example the crucial milling step takes placed in the presence of a mixture of macrocylic carbonate oligomers rather than in the presence of a high molecular weight polymer. The oligomer mixture is soluble in a wide variety of organic materials, and in addition, need not be dissolved since it is friable and will be broken down into small particles and widely dispersed among the pigment particles by milling. Conversion to high molecular weight polymer takes place after the solvent has been removed. Alternatively, coating may be accomplished in the absence of solvent using powder coating methods. This invention allows one to prepare charge generation layers with a polycarbonate binder for charge generation pigments. With the invention of the present application, in embodiments there is selected a mixture of macrocyclic carbonate oligomers, and this mixture is converted into a polymer after or simultaneously with the coating of the charge generation layer. The processes of the present invention and imaging members thereof allow the charge generation binder to be optionally crosslinked to provide tougher coatings that are more resistant to wear caused by toner development systems. In embodiments, the present invention is directed to the preparation of supporting substrates for layered imaging members which processes comprise the polymerization of macrocyclic oligomers to provide polycarbonate substrates where curling is minimized without the need for an anticurling layer as presently needed in many situations for layered imaging members. Curling of the substrate can result in adversely effecting the life of the imaging member, and can cause images of poor resolution. Curling is primarily caused by the mismatch of thermal expansion coefficients between substrates, such as MYLAR.RTM., with the polycarbonate of the charge transport layer. This can be overcome by coating another layer of polycarbonate onto the side of the polyester layer opposite the charge transport layer known as the anticurl backcoating. The present invention avoids the need for the second coating by producing a substrate of polycarbonate which will possess a similar thermal expansion characteristic to the polycarbonate of the charge transport layer. By avoiding the need for the anticurl coating, this invention eliminates an additional manufacturing step, material cost, and emissions of volatile organic compounds associated with the coating step. In addition, intrinsic internal stresses can also be created in the transport layer as a result of its inability to relax completely on drying when coated onto a polyester film. These stresses will influence the life of the photoreceptor and its failure modes and may be lessened when the supporting substrate is also a polycarbonate. These and other disadvantages can be avoided or minimized with the processes of the present invention. Also, in embodiments the present invention is directed to the fabrication of supporting substrates by the in situ polymerization of macrocyclic oligomers. The aforementioned photoresponsive imaging members can be negatively charged when the photogenerating layer is situated between the charge transport layer and the substrate, or positively charged when the charge transport layer is situated between the photogenerating layer and the supporting substrate. The layered photoconductive imaging members can be selected for a number of different known imaging and printing processes including, for example, electrophotographic imaging processes, especially xerographic imaging and printing processes wherein negatively charged or positively charged images are rendered visible with toner compositions of the appropriate charge. Generally, the imaging members are sensitive in the wavelength regions of from about 400 to about 850 nanometers, thus diode lasers can be selected as the light sources in some instances.
Layered imaging members with supporting substrates, such as aluminum, and polymeric materials, photogenerating and charge transport layers, including charge transport layers comprised of aryl diamines dispersed in polycarbonates, like MAKROLON.RTM., are known, reference for example U.S. Pat. No. 4,265,900, the disclosure of which is totally incorporated herein by reference. More specifically, in U.S. Pat. No. 4,265,900, the disclosure of which is totally incorporated herein by reference, there is illustrated an imaging member comprised of a supporting substrate, like aluminum or MYLAR.RTM., which have a tendency to curl, a photogenerating layer, and an aryl amine hole transport layer comprised of amine molecules dispersed in a polycarbonate. Examples of photogenerating layer components include trigonal selenium, metal phthalocyanines, vanadyl phthalocyanines, and metal free phthalocyanines. Additionally, there is described in U.S. Pat. No. 3,121,006 a composite xerographic photoconductive member comprised of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The binder materials disclosed in the '006 patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles.
Similar photoresponsive imaging members with squaraine photogenerating pigments are also known, reference U.S. Pat. No. 4,415,639. In this patent, there is illustrated a photoresponsive imaging member with a substrate, a hole blocking layer, an optional adhesive interface layer, an organic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, and a hole transport layer. As photoconductive compositions for the aforementioned member, there can be selected various squaraine pigments, including hydroxy squaraine compositions. Moreover, there is disclosed in U.S. Pat. No. 3,824,099 certain photosensitive hydroxy squaraine compositions.
The use of selected perylene pigments as photoconductive substances is also known. There is thus described in Hoechst European Patent Publication 0040402, DE3019326, filed May 21, 1980, the use of N,N'-disubstituted perylene-3,4,9,10-tetracarboxyldiimide pigments as photoconductive substances, and wherein the supporting substrate can be a metal like aluminum, or certain polymeric materials. Specifically, there is, for example, disclosed in this publication N,N'-bis(3-methoxypropyl)perylene-3,4,9,10-tetracarboxyldiimide dual layered negatively charged photoreceptors with improved spectral response in the wavelength region of 400 to 700 nanometers. A similar disclosure is revealed in Ernst Gunther Schlosser, Journal of Applied Photographic Engineering, Vol. 4, No. 3, page 118 (1978). There are also disclosed in U.S. Pat. No. 3,871,882 photoconductive substances comprised of specific perylene-3,4,9,10-tetracarboxylic acid derivative dyestuffs. In accordance with the teachings of this patent, the photoconductive layer is preferably formed by vapor depositing the dyestuff in a vacuum. Also, there is specifically disclosed in this patent dual layer photoreceptors with perylene-3,4,9,10-tetracarboxylic acid diimide derivatives, which have spectral response in the wavelength region of from 400 to 600 nanometers. Also, in U.S. Pat. No. 4,555,463, the disclosure of which is totally incorporated herein by reference, there is illustrated a layered imaging member with a chloroindium phthalocyanine photogenerating layer. In U.S. Pat. No. 4,587,189, the disclosure of which is totally incorporated herein by reference, there is illustrated a layered imaging member with a perylene pigment photogenerating component. Both of the aforementioned patents disclose an aryl amine component as a hole transport layer.
In copending application U.S. Ser. No. 537,714, the disclosure of which is totally incorporated herein by reference, there are illustrated photoresponsive imaging members with photogenerating titanyl phthalocyanine layers prepared by vacuum deposition. It is indicated in this copending application that the imaging members comprised of the vacuum deposited titanyl phthalocyanines on supporting substrates, such as certain polymeric materials and aryl amine hole transporting compounds, exhibit superior xerographic performance as low dark decay characteristics result and higher photosensitivity is generated, particularly in comparison to several prior art imaging members prepared by solution coating or spray coating, reference for example, U.S. Pat. No. 4,429,029 mentioned hereinbefore.
In copending patent application U.S. Pat. No. 5,300,392, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of photoconductive imaging members which comprises coating a supporting substrate with a photogenerator layer comprised of photogenerating pigments, and subsequently applying to the photogenerating layer a mixture comprised of charge transport molecules and cyclic oligomers, and wherein said mixture is heated to obtain a polycarbonate resin binder from said cyclic oligomers.
in copending application U.S. Pat. No. 5,300,393 is a process for the preparation of photoconductive imaging members which comprises coating a supporting substrate with a photogenerator layer comprised of photogenerating pigments and a mixture of cyclic oligomers wherein said mixture is heated to obtain a polycarbonate resin binder, and subsequently applying to the photogenerating layer a layer of charge transport molecules.
The disclosures of all of the aforementioned publications, laid open applications, copending applications and patents are totally incorporated herein by reference.